In manufacturing tires, the actual shaping of the tire is caused by inflating a rubber bag inside a green tire carcass to force the tire against the mold surface. Generally, there is substantial movement between the outer contact surface of the bladder, and the inner surface of the green tire during the expansion phase of the bladder prior to fully curing the tire. Likewise, there is also considerable relative movement between the outer contact surface of the bladder and the cured inner surface of the tire after the tire has been molded and vulcanized and the bladder has been collapsed and stripped from the inner tire surface.
It is essential that there be sufficient lubrication between the bladder and the inner tire surface in order to reduce friction between the bladder and the inside of the raw tire in order to allow for optimum slip of the bladder during the shaping process when the raw tire and bladder are in contact with one another. Finally, at the termination of the vulcanization cycle, the lubricant allows for the release and removal of the bladder from inside the tire.
Aqueous organopolysiloxane emulsions containing treated inorganic silicates have been used as lubricants for molding tires. These emulsions are described in, for example, U.S. Pat. No. 4,184,880 to Huber et al, in which an aqueous diorganopolysiloxane emulsion containing dispersed inorganic silicates which have been treated with organosilicon compounds to impart hydrophobic properties to the surfaces of the inorganic silicates have been employed as release agents for manufacturing tires. Also, U.S. Pat. No. 3,713,851 to Cekada describes aqueous organopolysiloxane emulsions which have been used as bag lubricants for molding tires in which the emulsion contains an alkyl methyl siloxane fluid including non-flowing gums, polyalkylene glycols, mica, carboxymethyl cellulose, lecithin and water. U.S. Pat. No. 4,431,452 to Comper et al discloses a lubricating composition for a tire bladder comprising (1) a hydroxylterminated polydimethylsiloxane having a viscosity up to about 25,000,000 centistokes at 25.degree. C., (2) a hydroxyl-terminated polydimethylsiloxane having a viscosity up to about 120,000 centistokes at 25.degree. C., (3) a polyalkylene glycol, (4) bentonite clay, and (5) a surfactant. U.S. Pat. No. 3,872,038 to Adams et al describes an aqueous emulsion which is useful as a bladder lubricant comprising (1) a silicone gum, (2) an organopolysiloxane fluid, (3) polyglycols, (4) mica, (5) lecithin, (6) sodium carboxymethyl cellulose, (7) emulsifying agents and (8) water.
A bladder lubricant is described in U.S. Pat. No. 4,359,340 to Comper et al in which an aqueous emulsion comprising (1) a polydimethylsiloxane having a viscosity up to about 25,000,000 centistokes at 25.degree. C., (2) a methylhydrogen silane having a viscosity of from 20 to 40 centistokes at 25.degree. C., or a dimethylhydrogen silane having a viscosity of from 80 to 120 centistokes at 25.degree. C., (3) a metal salt of an organic acid and (4) a surfactant is applied to the bladder surface.
An aqueous emulsion for treating organic fibers is described in U.S. Pat. No. 4,436,856 to Huhn et al in which the aqueous emulsion containing (1) an organopolysiloxane having at least two monovalent SiC-bonded organic radicals per molecule with a basic nitrogen atom, (2) an organopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (3) a catalyst for the condensation of Si-bonded condensable groups, (4) an emulsifier, and (5) a diorganopolysiloxane containing an Si-bonded terminal hydroxyl group.
A bladder release composition is described in U.S. Pat. No. 4,678,815 to Hoffman, in which the composition comprises (1) a hydroxyl-containing organopolysiloxane gum, (2) an organohydrogenpolysiloxane, (3) a lubricant having a melting range of from 25 to 80.degree. C., (4) a thickening agent, (5) a surfactant, and (6) water.
Aqueous organopolysiloxane emulsions employed heretofore as bladder lubricants in manufacturing tires have several disadvantages. For example, the preformulated aqueous organopolysiloxane emulsions have stability problems, such as ingredient settling, compaction and/or degradation during storage and/or during transportation, or upon inordinate temperature changes, such as freeze-thaw cycles.
In addition, many of the compositions, particularly those with hydroxyl-containing organopolysiloxanes and methylhydrogenpolysiloxane fluids have a tendency to crosslink. When the crosslink density increases the number of releases also increases; however, an increase in crosslinked density results in a reduction in lubricity.
In order to improve the lubricity and improve venting between the bladder and the inside of the tire, it has been necessary to either increase the amount of filler or increase the amount of silicone polymer present in the composition. When the amount of filler is increased, settling and compaction become a problem.
It has been found that the addition of mica, a small amount, for example, up to about one percent based on the weight of the emulsion, will enhance the lubricity of the crosslinked composition; however, when the compositions contain methylhydrogenpolysiloxanes, the composition may release hydrogen. Therefore, the addition of mica to a composition will compensate for increased crosslinked density by enhancing the lubricity of the composition.
Also, some of the organopolysiloxane compositions contain catalysts which have a tendency to accelerate the degradation of the resultant emulsion and release hydrogen as a by-product.
Furthermore, many of the aqueous organopolysiloxane compositions have to be applied to the bladder just prior to shaping the tire, otherwise good lubricity and release properties are not achieved.
As a result of this invention, it is now possible to prepare a composition having increased crosslinked density with improved lubricity. Also, it is possible to prepare aqueous organopolysiloxane emulsions which do not release hydrogen during storage. Moreover, the aqueous organopolysiloxane emulsions of this invention can be applied to the inside of a green tire carcass and allowed to stand overnight without affecting the release properties. Furthermore, the inside of a green tire carcass can be coated with the aqueous organopolysiloxane emulsions away from the press area and then transferred to the press area where they are molded.
Therefore, it is an object of the present invention to provide an aqueous organopolysiloxane composition which may be used as a bladder lubricant. Another object of the present invention is to provide a composition which is stable over a long period of time. Another object of the present invention is to provide an aqueous organopolysiloxane emulsion which will give numerous releases per application. Still another object of the present invention is to provide an aqueous organopolysiloxane emulsion having improved lubricity irregardless of the crosslinked density. A further object of the present invention is to provide a method for preparing a stable aqueous organopolysiloxane emulsion. Still a further object of the present invention is to provide an aqueous emulsion containing mica and an organohydrogenpolysiloxane which is stable over long periods of time.